12 March, 2016

Newly-discovered bacterium can break down, metabolize plastic

According to
a group of biologists in Japan, the newfound species — named
Ideonella sakaiensis 201-F6 — breaks down the plastic by using two
enzymes to hydrolyze poly[ethylene terephthalate], or PET.

PET is a
condensation polymer used in plastic that is highly resistant to
biodegradation. It is industrially produced by either terephthalic
acid or dimethyl terephthalate with ethylene glycol.

To date,
very few species of fungi – but no bacteria – have been found to
break down this polymer.

The Japanese
team, led by Dr. Kohei Oda from the Kyoto Institute of Technology and
Dr. Kenji Miyamoto from Keio University, collected 250 samples of PET
debris and screened for bacterial candidates that depend on PET film
as a primary source of carbon for growth.

They
identified Ideonella sakaiensis 201-F6, which could nearly completely
degrade a thin film of PET after six weeks at a temperature of 86
degrees Fahrenheit (30 degrees Celsius).

Further
investigation identified an enzyme, ISF6_4831, which works with water
to break down PET into an intermediate substance, which is then
further broken down by a second enzyme, ISF6_0224.

“By
screening natural microbial communities exposed to PET in the
environment, we isolated a novel bacterium, Ideonella sakaiensis
201-F6, that is able to use PET as its major energy and carbon
source,” the scientists explained.

“When
grown on PET, this strain produces two enzymes capable of hydrolyzing
PET and the reaction intermediate, mono(2-hydroxyethyl) terephthalic
acid.”

“Both
enzymes are required to enzymatically convert PET efficiently into
its two environmentally benign monomers, terephthalic acid and
ethylene glycol.”

Remarkably,
ISF6_4831 and ISF6_0224 seem to be highly unique in their function
compared to the closest related known enzymes of other bacteria,
raising questions of how these plastic-eating bacteria evolved.